// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef CONTENT_BROWSER_HISTOGRAM_CONTROLLER_H_
#define CONTENT_BROWSER_HISTOGRAM_CONTROLLER_H_

#include <string>
#include <vector>

#include "base/macros.h"
#include "base/memory/singleton.h"

namespace content {

class HistogramSubscriber;

// HistogramController is used on the browser process to collect histogram data.
// Only the browser UI thread is allowed to interact with the
// HistogramController object.
class HistogramController {
public:
    // Returns the HistogramController object for the current process, or NULL if
    // none.
    static HistogramController* GetInstance();

    // Normally instantiated when the child process is launched. Only one instance
    // should be created per process.
    HistogramController();
    virtual ~HistogramController();

    // Register the subscriber so that it will be called when for example
    // OnHistogramDataCollected is returning histogram data from a child process.
    // This is called on UI thread.
    void Register(HistogramSubscriber* subscriber);

    // Unregister the subscriber so that it will not be called when for example
    // OnHistogramDataCollected is returning histogram data from a child process.
    // Safe to call even if caller is not the current subscriber.
    void Unregister(const HistogramSubscriber* subscriber);

    // Contact all processes and get their histogram data.
    void GetHistogramData(int sequence_number);

    // Notify the |subscriber_| that it should expect at least |pending_processes|
    // additional calls to OnHistogramDataCollected().  OnPendingProcess() may be
    // called repeatedly; the last call will have |end| set to true, indicating
    // that there is no longer a possibility for the count of pending processes to
    // increase.  This is called on the UI thread.
    void OnPendingProcesses(int sequence_number, int pending_processes, bool end);

    // Send the |histogram| back to the |subscriber_|.
    // This can be called from any thread.
    void OnHistogramDataCollected(
        int sequence_number,
        const std::vector<std::string>& pickled_histograms);

private:
    friend struct base::DefaultSingletonTraits<HistogramController>;

    // Contact PLUGIN and GPU child processes and get their histogram data.
    // TODO(rtenneti): Enable getting histogram data for other processes like
    // PPAPI and NACL.
    void GetHistogramDataFromChildProcesses(int sequence_number);

    HistogramSubscriber* subscriber_;

    DISALLOW_COPY_AND_ASSIGN(HistogramController);
};

} // namespace content

#endif // CONTENT_BROWSER_HISTOGRAM_CONTROLLER_H_
